1. Technical Field
The present invention relates to a variable capacitance circuit, an oscillator circuit, a vibratory device, an electronic apparatus, a moving object, a method of manufacturing a vibratory device, and so on.
2. Related Art
The variable capacitance circuit includes a variable capacitance element, and is capable of adjusting the capacitance value by varying a control voltage to be applied to the variable capacitance element. The variable capacitance element is, for example, a varicap (variable capacitance diode), and the varicap varies in capacitance value in accordance with an inter-terminal voltage (equal to a control voltage in the case in which one of the terminals is in the ground voltage). The variable capacitance circuit is used as a load capacitance of, for example, an oscillator circuit, and is used for adjusting the frequency (hereinafter also referred to as an oscillation frequency) of an oscillation signal in some cases.
For example, the invention disclosed in JP-A-2003-258553 (Document 1) includes the variable capacitance circuit in the oscillator circuit, and can suppresses the influence of the voltage fluctuation with respect to the oscillation frequency by switching a stationary voltage to be applied to each of the variable capacitance elements.
Here, when manufacturing the oscillator including, for example, an oscillator element, it is necessary to adjust the shift of the oscillation frequency based on the individual variation in the oscillator element to output a desired frequency. On this occasion, according to the oscillator circuit of Document 1, when switching the stationary voltage, the voltage-oscillation frequency characteristic varies significantly. Therefore, since the frequency variable range also varies significantly in some cases, a complicated adjustment becomes necessary in general, and it is unachievable to make it easy to adjust the oscillation frequency.
Further, a variable capacitance circuit used for the oscillator of JP-A-2003-324316 (Document 2) is for switching the voltage to be applied to the variable capacitance element between a stationary voltage and the power supply voltage to control the capacitance value of the variable capacitance to be the maximum value or the minimum value. However, since the voltage-oscillation frequency characteristic significantly varies due to the switching of the voltage (see, e.g., FIG. 2B of Document 2), and thus the frequency variable range also varies in some cases, it is unachievable to make it easy to adjust the oscillation frequency.
Here, among the variable capacitance circuits, there exist some circuits in which the variable capacitance element itself can be unconnected using a switch circuit. However, if the number of the variable capacitance elements to be unconnected is varied, the voltage-oscillation frequency characteristic also changes dramatically. Therefore, even by using such a variable capacitance circuit as described above as the load capacitance of the oscillator circuit, it is unachievable to make it easy to adjust the oscillation frequency.
On the contrary, it can be said that the complicated adjustment procedure is unnecessary if certain regularity exists in the change when switching the voltage-oscillation frequency. Further, if the oscillation frequency can be varied around a certain frequency (hereinafter also referred to as a specific frequency), the adjustment of the oscillation frequency can easily be executed.